1. Field of the Invention
The present invention relates to user-programmable antifuse devices. More particularly, the present invention relates to several embodiments of a raised tungsten plug antifuse and to methods for fabricating such antifuses.
2. The Prior Art
Various antifuse structures are known in the prior art. The prior-art antifuses may be divided into two groups. A first group includes those antifuses in which the lower electrode comprises a conductive region in a semiconductor substrate and the upper electrode comprises a layer above the substrate. A layer of antifuse material disposed between the lower and upper electrodes usually comprises a single dielectric layer or a plurality of dielectric layers. An example of such an antifuse is shown in U.S. Pat. No. 4,823,181 to Mohsen et al., and U.S. Pat. No. 4,543,594 to Mohsen et al.,
A second group of antifuses comprises antifuses in which both electrodes are disposed in layers above the surface of a substrate which may be either a conducting material, a semiconductor material, or an insulating material. The electrodes may comprise materials such as metal layers or polysilicon layers. A layer of antifuse material disposed between the lower and upper electrodes may comprise a single dielectric layer, a plurality of dielectric layers, a layer of a material such as amorphous silicon, or a layer of a material such as amorphous silicon in combination with one or more dielectric layers. The second group of antifuses is more closely associated with the present invention.
Examples of above-the-substrate antifuses include those disclosed in U.S. Pat. No. 5,070,384 to McCollum et al., U.S. Pat. No. 5,175,715 to Husher et al., U.S. Pat. No. 5,181,096 to Forouhi, U.S. Pat. No. 5,272,101 to Forouhi et al., and U.S. Pat. No. 5,196,724 to Gordon et al.,
It is an object of the present invention to provide an improved above-the-substrate antifuse and methods for fabricating such an antifuse.